Cathodic protection systems are generally in use for corrosion protection of metal structures. Many current cathodic protection devices employ the use of corrosion coupons in order to measure conditions of a particular system, more specifically the corrosivity of tanks and various types of operating equipment. However, these devices are subject to a number of drawbacks, many of which affect the most important objective of the device: providing an accurate measurement of the corrosive nature of a particular environment with respect to a specific type of material.
Various factors relating to both corrosion coupons and cathodic protection devices are relevant in measuring the corrosive nature of a particular environment. With regards to coupons, it is necessary that they are placed in a representative location within the system being monitored such that the location is representative in temperature, pressure, water chemistry, chemical additions, bacterial populations, and solids loading. It is also important that the coupon be electrically isolated from both the cathodic protection device and the system to be monitored in order to prevent galvanic effects that could potentially influence the coupon reading.
The necessary calculation that leads to the measurement of the corrosion rate is based upon the surface area of the coupon. Currently, many of the corrosion coupons in use are in the form of rings, as disclosed in U.S. Pat. No. 4,208,264 (Polak), and thus result in poor surface area for control of the calculation leading to the measurement of corrosion. Therefore, it is advantageous to provide a coupon with adequate exposure of surface area for control of this specific calculation.
In order to expose the coupon to the particular environment measured, it is necessary for coupon placement to be on the outside of the housing unit, which contains the reference cell. Means of placing or mounting the coupons on the housing unit have generally included the use of metallic nuts and/or bolts as fasteners, as disclosed in U.S. Pat. No. 4,928,760 (Freitas). In addition to using nuts and bolts for fastening the coupons to the device, nuts and bolts are also used in fastening wiring and leads to the coupons. Issues arise, however, when the metallic nuts and bolts begin to corrode themselves. Not only is the life of the device decreased, but the corrosion of the nuts and/or bolts begins to interfere with the readings taken by the coupon to calculate the corrosion measurements. Therefore, alternative means to fasten various components of the device are desirable.
Further, the reference cell housing portion of many prior art devices consists of a porous ceramic vessel, an example of which is disclosed in U.S. Pat. No. 4,208,264 (Polak). The porous nature of the ceramic vessel, accompanied with exposure to the outside environment, allows for water from the outside environment to flow through the vessel and into the housing unit. It also allows for penetration of conductive material contained within the housing unit, thus resulting in loss of conductive material to the outside environment. Leakage into the vessel also results when the coupons are not properly sealed within the coupon jacket. Existing methods of sealing the coupon within its housing component result in gaps around the outside of the coupon, thus allowing for water from the outside environment to enter causing further corrosion to the coupon. Therefore, a method of improving the sealing of the coupon within its housing is needed.
Overall, there has not been available to date any device that provides the improvements necessary for providing accurate exposure of coupon surface area, reducing metal galvanic corrosion, eliminating loss of conductive material from within the housing of the device, and sealing and preventing leaks from the housing of the device.